An access control system controls the lock. But controlling the lock only matters if the system also knows the state of the door. Is it open? Is it closed? Is someone coming through it right now? Without answers to those questions, the system is blind, it can unlock a door, but it can’t tell whether the door actually closed and re-secured afterward.
That’s where door position switches and request-to-exit (REX) sensors come in. They’re the inputs that tell the controller what’s happening at the door, in real time.
Door Position Switches (DPS)
A door position switch is a magnetic contact sensor. One half, the reed switch, mounts on the frame. The other half, the magnet, mounts on the door. When the door is closed, the magnet is close enough to the reed switch to hold it in one state. When the door opens, the magnet moves away and the switch changes state. The controller reads that change and knows: the door is open.
The DPS is the most basic monitoring input. Without it, the controller can unlock the door, but it has no way to know whether someone propped it open, whether it failed to close, or whether it was forced. The DPS turns a blind lock into a monitored opening.
On commercial aluminum storefront doors, the DPS is typically surface-mounted on the top rail of the frame, with the magnet on the top of the door. Concealed versions are available, where the switch and magnet are embedded inside the door and frame extrusion, but these require machining the aluminum and are harder to service.
Door Forced Open (DFO) Alarms
When the controller sees the DPS change from closed to open without an unlock command, that’s a door-forced-open event. The system was supposed to unlock the door first, someone was supposed to present a credential, but the DPS changed without that step. That means the door was forced. The controller logs the event and can trigger an alarm.
DFO alarms only work with a DPS. Without the switch, the controller has no way to distinguish between a door that was unlocked normally and one that was forced.
Door Propped Open (DPO) Alarms
When the DPS shows the door is open for longer than a set timeout, typically 30 to 60 seconds, the controller flags a door-propped-open event. Someone held the door, wedged it, or it failed to close. The system logs the event and can alert security or property management.
Request-to-Exit (REX) Sensors
A REX sensor tells the controller that someone is approaching the door from the inside. On an egress door, a door that people need to be able to exit freely, the REX sensor ensures the system unlocks (or the magnetic lock releases) when someone approaches, without requiring a credential.
There are two common types:
Passive infrared (PIR) REX detects body heat and motion. When someone walks toward the door from inside, the PIR sensor triggers and the controller releases the lock. PIR sensors are the most common type because they’re reliable, don’t require physical contact, and work well in most environments.
Mechanical REXtypically a push bar or a paddle, requires the person to physically push something to exit. These are used on doors where the REX needs to be intentional, not just motion-triggered. A mechanical REX is sometimes paired with a PIR as a redundant system.
Why REX Matters for Egress Compliance
On a door with a magnetic lock, the REX sensor is the primary means of free egress. If the maglock doesn’t release, people can’t get out, which is a life safety violation. The REX sensor has to be reliable, and on listed systems, it has to fail safe: if the sensor fails, the door unlocks.
Building codes, including the International Building Code and NFPA 101, Life Safety Code, require that egress doors allow free exit at all times, without special knowledge or effort. An access control system that requires a credential to exit is non-compliant. The REX sensor solves this: the person walks toward the door, the sensor detects them, and the lock releases.
How DPS and REX Work Together
The two sensors give the controller a complete picture of what’s happening at the door:
- Normal entry: Credential presented → controller unlocks → DPS changes to open (person enters) → DPS changes to closed (door swings shut) → controller re-locks.
- Normal exit: REX detects person approaching → controller releases lock → DPS changes to open → DPS changes to closed → controller re-locks.
- Forced entry: No credential presented → DPS changes to open → controller flags DFO alarm.
- Propped door: DPS stays open past timeout → controller flags DPO alarm.
Without both sensors, the system can’t distinguish between these scenarios. With both, every door event is logged, categorized, and actionable.
What Fails
DPS misalignment. If the door shifts on its hinges, the magnet on the door moves away from the reed switch on the frame, even when the door is closed. The controller reads the door as open when it’s actually closed, which triggers false DFO and DPO alarms. The fix is correcting the door alignment first, then re-aligning the DPS.
REX dead spots. PIR sensors have a coverage pattern, a cone of detection. If the sensor is mounted too high, too far from the door, or aimed incorrectly, there’s a dead zone where a person approaching the door isn’t detected. The door doesn’t unlock, and the person is trapped. The fix is repositioning the sensor and testing the coverage by walking the approach path.
Wiring failures. Both sensors run low-voltage wiring back to the controller. On aluminum storefront doors, the wiring routes through the frame extrusion and across the threshold, a path that’s vulnerable to chafing, water intrusion, and physical damage. A broken wire means the sensor goes dark, and the controller can’t read the door state.
What Pro Locksmith Does
Pro Locksmith LLC installs and services door position switches, REX sensors, and complete access control monitoring systems for commercial properties throughout Broward County and Miami-Dade, including Fort Lauderdale, Hollywood, Pembroke Pines, Davie, Pompano Beach, Coral Springs, and Miami. We design systems that maintain free egress at all times, with mechanical lock backup independent of the electronic system. Licensed and insured. Flat-rate pricing quoted up front. COI provided. Employees, not subcontractors.
If your access control system is generating false alarms or your REX sensors aren’t reliably detecting exit, call Pro Locksmith LLC at (954) 406-8266.
Sources
- NFPA 101, Life Safety Code (egress requirements)
- International Building Code, Chapter 10 (Means of Egress)
- ADA Standards for Accessible Design, Section 404
Closed, Latched and Locked Are Three Different Things
A door position switch answers one question: is the door in the frame? It does not tell the controller whether the latch actually engaged or whether the lock is secured. A door can be pushed closed against the frame, satisfy the DPS, and still be unlatched because the latch bolt hit the strike and did not fall into place. On a door with an electric strike, the strike can also fail to relock after a valid entry. In both cases the DPS reports “closed” and the door is effectively open.
For openings where that gap matters, additional monitoring switches are available:
- Latch bolt monitoring reports whether the latch bolt is extended into the strike.
- Strike monitoring, on many electric strikes, reports whether the strike keeper is locked or unlocked and whether a latch is sitting in it.
- Lock status sensing on magnetic locks reports whether the armature plate is fully seated against the magnet and holding at its rated force.
Combining the DPS with one of these gives the controller a much truer picture. Many facilities only discover the gap after an incident, when the logs show a door as closed all night even though it could be pulled open by hand.
How the Switch Is Wired Matters
Door position switches are simple devices, but how they are wired to the controller affects how reliable and tamper resistant the monitoring is.
Normally closed and normally open contacts
Most door contacts are available in configurations where the circuit is closed when the door is closed, or the reverse. Access control installations generally use the configuration that opens the circuit when the door opens, because a cut wire then looks the same as an open door and gets reported rather than hidden.
Supervised inputs
Many controllers support supervised inputs, which use end-of-line resistors so the controller can tell the difference between a closed door, an open door, a cut wire and a shorted wire. Without supervision, someone who shorts the wires at the frame can make an open door look closed. With supervision, that tampering generates its own alarm. If your controller supports supervised inputs and they are not being used, it is worth asking why.
Choosing the Right Switch for the Door
Hollow metal doors and frames
Steel doors in steel frames often use recessed contacts drilled into the top of the door and the head of the frame. These are concealed and hard to tamper with. The switch must be rated for use in steel, since the metal around it can affect the magnetic field and shorten the gap at which the switch changes state.
Wood doors
Wood doors in office suites usually take a recessed contact as well, installed in the top edge of the door. It is a clean installation but should be planned so that the wiring path through the frame is accessible for service.
Overhead and roll-up doors
Warehouses and loading docks often need the roll-up and sectional overhead doors monitored too. These doors move more than a swinging door, so standard contacts do not work well. Heavy-duty floor-mounted contacts with armored cable and a wide gap rating are designed for this, and they are mounted where a forklift or dock traffic will not destroy them.
Pairs of doors
On double doors, each leaf needs its own switch. Monitoring only the active leaf leaves the inactive leaf unmonitored, and if its flush bolts are not engaged, it can be pushed open without the system ever knowing.
Shunting: How REX Prevents False Alarms on Mechanical Exit Doors
Not every REX input is used to release a lock. On many doors, the lock is mechanical on the inside, such as a lever or a panic bar that always lets people out. In that case the REX has a different job: it tells the controller that the upcoming door opening is a legitimate exit, so the controller shunts, or ignores, the DPS change for a set time instead of calling it a forced door.
Without this, every person who walks out through a panic device would generate a door forced alarm, and staff would quickly learn to ignore alarms entirely. With it, forced door alarms mean something again. Many exit devices can be ordered with a built-in request-to-exit switch that activates when the push bar is pressed, which is a reliable way to handle shunting on exit doors because it is triggered by the actual exit motion rather than by someone walking near the door.
Alarm Fatigue Is a Security Problem
A monitoring system that cries wolf is not much better than no monitoring. When a front desk or security team sees dozens of false forced and propped alarms every day, they stop looking. Then a real forced entry blends in with the noise.
The usual sources of false alarms are fixable:
- A door that does not close all the way on its own because the closer is weak or poorly adjusted
- A DPS gap that is too tight for a door that moves slightly in wind or with air pressure changes
- A REX sensor that is missing people who push the bar before the sensor sees them
- A propped door timer set too short for a door where deliveries come through
- Wiring that intermittently loses contact at a door loop or hinge
Going door by door through the alarm history usually points to a handful of openings responsible for most of the noise. Fixing those restores the value of the whole system.
Door Closers Are Part of the Monitoring System
A door position switch can only report closed if the door actually closes. Door closers weaken over time, arms loosen, and the adjustment valves drift. In South Florida, air conditioning pressure in large buildings can also push against exterior doors, so a closer that was fine in the winter may not pull the door into the latch in the summer. Checking and adjusting closers is one of the most effective ways to reduce propped door alarms and make sure doors actually latch.
Weather, Water and Coastal Buildings
Exterior contacts on buildings near the coast face salt air and wind-driven rain. Surface-mounted contacts on storefront frames can corrode, and water finding its way into a frame can damage wiring or the switch itself. Using contacts rated for the environment, sealing wire entry points and routing wiring so water drains away from connections all help. After a major storm, it is worth testing every exterior DPS and REX, since a door that was forced by wind pressure or a frame that shifted can throw alignment off.
A Simple Testing Routine
Monitoring hardware should be tested regularly, not just when something goes wrong. A basic routine for a facility manager might look like this:
- Open each monitored door without a credential and confirm the forced door alarm appears at the controller or monitoring station.
- Hold each door open past the propped door timer and confirm the propped alarm appears.
- Walk the exit path at each REX-controlled door, approaching at a normal pace and from the side, and confirm the door releases or shunts every time.
- Close each door gently and confirm it latches and reports closed.
- Review the event log for doors that report frequent open and close events at odd times, which can indicate a failing switch.
Keep a record of each test with the date and results. If a door fails, mark it for service promptly, especially if it is an egress door.
Tailgating Is Not Something a DPS Can Stop
Door monitoring tells you that a door opened, not how many people walked through it. If one employee badges in and a second person follows before the door closes, the DPS sees one normal entry. Preventing tailgating takes a combination of staff awareness, faster closers, camera coverage at key doors and, in higher-security areas, turnstiles or other entry controls. It is worth being realistic about what door switches can and cannot do when planning a system.
Documenting Each Monitored Opening
When monitoring hardware is installed piecemeal over the years, nobody has a full picture of what each door is supposed to report. A simple door schedule solves that. For every monitored opening, record the door number and location, the lock type, the DPS type and where it is mounted, whether a REX device is installed and whether it releases the lock or only shunts the alarm, the propped door timer setting, and any latch or lock status monitoring. Note where the wiring junctions are, especially on storefront frames and door loops.
That schedule pays for itself the first time a door starts misbehaving. The technician knows what the door should be doing before arriving, the right parts come on the first visit, and changes made during service are written down instead of lost. It also helps when a building changes hands or a new property manager takes over and needs to understand what the previous owner installed.
Work With the Local Authority on Egress Doors
Any change that affects how people exit a building, including adding a maglock, changing REX devices or adjusting release timing, should be reviewed with the authority having jurisdiction, which is usually the local fire marshal or building department. Requirements for delayed egress, fire alarm release and signage vary by occupancy and by jurisdiction, and the people enforcing them are the ones whose interpretation counts.
Where We Service Door Monitoring
We install, align and troubleshoot door position switches, request-to-exit devices and related monitoring hardware for offices, retail storefronts, warehouses and multi-tenant buildings across Broward County and Miami-Dade, including Aventura, North Miami, Miami, Coral Gables and Coconut Grove. For commercial properties we also cover Boca Raton, Delray Beach, Boynton Beach, Lake Worth Beach and West Palm Beach. Whether you are chasing false alarms on a single storefront or reviewing every monitored door in a building, we start by walking each opening and testing what it actually reports.